Vineesh V, Geography

It is the process of removing the influence of the atmosphere from remotely sensed images so that the data accurately represent the true reflectance of Earth's surface . When a satellite sensor captures an image, the radiation reaching the sensor is affected by gases, water vapor, aerosols, and dust in the atmosphere. These factors scatter and absorb light, changing the brightness and color of the features seen in the image. Although these atmospheric effects are part of the recorded signal, they can distort surface reflectance values , especially when images are compared across different dates or sensors . Therefore, corrections are necessary to make data consistent and physically meaningful. 🔹 Why Do We Need Atmospheric Correction? To retrieve true surface reflectance – It separates the surface signal from atmospheric influence. To ensure comparability – Enables comparing images from different times, seasons, or sensors. To improve visual quality – Remo...

  Radiometric correction is the process of removing sensor and environmental errors from satellite images so that the measured brightness values (Digital Numbers or DNs) truly represent the Earth's surface reflectance or radiance. In other words, it corrects for sensor defects, illumination differences, and atmospheric effects. 1. Detector Response Calibration Satellite sensors use multiple detectors to scan the Earth's surface. Sometimes, each detector responds slightly differently, causing distortions in the image. Calibration adjusts all detectors to respond uniformly. This includes: (a) De-Striping Problem: Sometimes images show light and dark vertical or horizontal stripes (banding). Caused by one or more detectors drifting away from their normal calibration — they record higher or lower values than others. Common in early Landsat MSS data. Effect: Every few lines (e.g., every 6th line) appear consistently brighter or darker. Soluti...

A pandemic disaster is a global or widespread outbreak of an infectious disease that causes mass illness, death, and disruption of social and economic systems across multiple countries or continents. Terminology: Epidemic: Outbreak of disease in a specific community or region. Pandemic: Epidemic that spreads across countries or continents. Endemic: Disease constantly present in a region (e.g., malaria in parts of Africa). Outbreak: Sudden increase in disease cases in a limited area. So, a pandemic becomes a disaster when the disease's scale and impact overwhelm healthcare systems and disrupt societies. Conceptual Understanding Pandemic disasters are biological hazards , categorized under man-made or natural–biological disasters because they are caused by natural pathogens but spread or intensified by human actions such as globalization, urbanization, and poor public health infrastructure. Pandemic disasters sit at the intersection of ...

Aspect Man-Made Disaster Complex Disaster Pandemic Disaster 1️⃣ Definition A catastrophic event caused directly or indirectly by human actions , such as industrial accidents, pollution, or war. A disaster that results from the interaction of natural hazards and human-induced factors (like conflict, poverty, poor governance). A global or widespread outbreak of infectious disease causing severe health, social, and economic disruption. 2️⃣ Nature Anthropogenic / Technological Hybrid (Natural + Human) Biological / Health-related 3️⃣ Primary Cause Human error, negligence, industrial failure, war, terrorism, pollution. Natural hazard combined with vulnerability, weak capacity, or political instability. Transmission of infectious pathogen (virus, bacteria) among humans; amplified by globalization and mobility. 4️⃣ Origin of Hazard Human-made (technological, industrial, or social activity). Both natural processes (earthquakes, droughts) and human systems (conflict, poor planning). Natura...

A Complex Disaster is a situation in which a natural disaster interacts with human-made (anthropogenic) factors —such as conflict, poor governance, poverty, or environmental degradation— to worsen its impact . In simple terms: Complex disasters occur when natural hazards meet human vulnerability and socio-political instability. These are sometimes called "complex emergencies" because they require both humanitarian aid and political solutions . Terminology and Key Concepts Term Meaning Complex Emergency A severe humanitarian crisis caused by a combination of natural disaster, war, or governance failure. Vulnerability The degree to which people or systems are susceptible to harm due to physical, social, economic, or environmental factors. Resilience The capacity to recover quickly from hazards and maintain function. Exposure The presence of people or assets in areas prone to hazards. Disaster Risk Nexus The interconnection between natural, social, economic, an...

  A man-made disaster (also called a technological disaster or anthropogenic disaster ) is a catastrophic event caused directly or indirectly by human actions , rather than natural processes. These disasters arise due to negligence, error, industrial activity, conflict, or misuse of technology , and often result in loss of life, property damage, and environmental degradation . Terminology: Anthropogenic = originating from human activity. Technological hazard = hazard caused by failure or misuse of technology or industry. 🔹 Conceptual Understanding Man-made disasters are part of the Disaster Management Cycle , which includes: Prevention – avoiding unsafe practices. Mitigation – reducing disaster impact (e.g., safety regulations). Preparedness – training and planning. Response – emergency actions after the disaster. Recovery – long-term rebuilding and policy correction. These disasters are predictable and preventable through strong...

When satellite or aerial images are captured, they often contain distortions (errors in shape, scale, or position) caused by many factors — like Earth's curvature, satellite motion, terrain height (relief), or the Earth's rotation . These distortions make the image not properly aligned with real-world coordinates (latitude and longitude). 👉 Geometric correction is the process of removing these distortions so that every pixel in the image correctly represents its location on the Earth's surface. After geometric correction, the image becomes geographically referenced and can be used with maps and GIS data. Types  1. Systematic Correction Systematic errors are predictable and can be modeled mathematically. They occur due to the geometry and movement of the satellite sensor or the Earth. Common systematic distortions: Scan skew – due to the motion of the sensor as it scans the Earth. Mirror velocity variation – scanning mirror moves at a va...

🌑  Blackbody in Remote Sensing 🔹 Definition: A blackbody is an idealized object that absorbs all incident electromagnetic radiation —regardless of wavelength or direction—and re-emits it perfectly according to its temperature. It is a perfect emitter and perfect absorber . 🔹 Reflection: For a blackbody, reflection = 0 (It does not reflect any incoming radiation.) 🔹 Absorption: Absorptivity (α) = 1 It absorbs 100% of the radiation incident upon it. 🔹 Albedo: Albedo = 0 Since no radiation is reflected, the surface appears perfectly dark. 🔹 Emissivity (ε): Emissivity = 1 A blackbody emits the maximum possible radiation at a given temperature (as described by Planck's Law ). 🔹 Remote Sensing Relevance: In remote sensing, the concept of a blackbody helps in: Calibrating thermal sensors . Understanding radiation–temperature relationships (Stefan–Boltzmann and Wien's Laws). Comparing real objects' emissivi...

In remote sensing , understanding black body and grey body behavior is fundamental for interpreting thermal infrared (TIR) data — especially from sensors that measure surface temperature or emitted energy from the Earth's surface. Thermal remote sensing relies on the principle that all objects with temperatures above absolute zero (0 K) emit electromagnetic radiation according to their temperature and emissivity. Black Body in Remote Sensing A black body is an idealized surface that: Absorbs all incident radiation (absorptivity = 1). Reflects none (reflectivity = 0). Emits the maximum possible thermal radiation at any given temperature and wavelength. This emission follows Planck's Law , Stefan–Boltzmann Law , and Wien's Displacement Law : Planck's Law: Describes how the intensity of radiation varies with wavelength for a given temperature. Stefan–Boltzmann Law: ( E = \sigma T^4 ) — total emitted energy is proportional to t...

Remote Sensing means collecting information about the Earth's surface without touching it , usually using satellites, aircraft, or drones . There are different types of remote sensing based on the energy source and the wavelength region used. 🛰️ 1. Active Remote Sensing 📘 Concept: In active remote sensing , the sensor sends out its own energy (like a signal or pulse) to the Earth's surface. The sensor then records the reflected or backscattered energy that comes back from the surface. ⚙️ Key Terminology: Transmitter: sends energy (like a radar pulse or laser beam). Receiver: detects the energy that bounces back. Backscatter: energy that is reflected back to the sensor. 📊 Examples of Active Sensors: RADAR (Radio Detection and Ranging): Uses microwave signals to detect surface roughness, soil moisture, or ocean waves. LiDAR (Light Detection and Ranging): Uses laser light (near-infrared) to measure elevation, vegetation...

1. Foundational Phase (Early 1970s – Early 1980s) Objective: To explore the potential of space-based observation for national development. 1972: The Space Applications Programme (SAP) was initiated by the Indian Space Research Organisation (ISRO), focusing on applying space technology for societal benefits. 1975: The Department of Space (DoS) was established, providing an institutional base for space applications, including remote sensing. 1977: India began aerial and balloon-borne experiments to study Earth resources and assess how remote sensing data could aid in agriculture, forestry, and hydrology. 1978 (June 7): Bhaskara-I launched by the Soviet Union — India's first experimental Earth Observation satellite . Payloads: TV cameras (for land and ocean surface observation) and a Microwave Radiometer. Significance: Proved that satellite-based Earth observation was feasible for India's needs. 1981 (November 20): Bhaskara-II launche...

LiDAR (Light Detection and Ranging) is an active remote sensing technology that measures distances by illuminating a target with laser pulses and analyzing the time it takes for the reflected light to return. Unlike passive systems (e.g., cameras, multispectral sensors), LiDAR provides its own energy source (laser), allowing it to operate both day and night and even penetrate through vegetation canopies . 🔹 How LiDAR Works (Step-by-Step Process) Laser Pulse Emission The system emits rapid, short pulses of laser light (commonly in the near-infrared wavelength, 1064 nm ). Some systems emit up to hundreds of thousands of pulses per second . Interaction with Target Surface The laser beam strikes objects such as vegetation, buildings, or bare ground. Depending on the object's structure, part of the pulse may scatter or reflect. Return Signal Detection The sensor records multiple returns : First Return → typically vegetation canopy tops. ...